Electrostatic coating apparatus



Oct. 5, 1954 IN V EN TOR.

JAMES C. MARSH BY W7 ZXW Aflorney Patented Oct. 5, 1954 ELECTROSTATICCOATING APPARATUS James C. Marsh, Indianapolis, Ind., assignor toRansburg Electro-Coating Corn, Indianapolis, Ind., a corporation ofIndiana Application October 4, 1951, Serial No. 249,764

6 Claims.

This invention relates to the electrostatic coating of articles.

Articles such as automobile steering wheels have previously been coatedby electrostatically depositing an atomized paint on them as they aremoved in an elongated coating zone as is shown in the copendingapplication of William A. Starkey, Serial No. 689,116, filed August 8,1946, now abandoned. While coating such articles by the method justreferred to obtained markedly improved eiiiciency over conventionalmechanical and hand spray methods, some paint still passed through theelectrostatic field without being deposited on the articles, andtherefore spray booths were still required for surrounding the coatingstation to carry away the overspray.

In order to improve still further the efficiency in applying coatingmaterial to such articles, electrostatic atomizing apparatus such asthat illustrated in the copending application of E. M. Ransburg, SerialNo. 143,994, filed February 13, 1950, was tried. However, it was foundthat while the efficiency of depositing the coating material sprayed onarticles being coated with such apparatus was increased such that 97percent of the coating material sprayed was deposited onto the article,the distribution of the deposited coat-- ing material was sumcientlyuneven as to make the process unsatisfactory for commercial use.

Therefore, it is an object of this invention to provide novelelectrostatic apparatus for applying a coating to three dimensionalarticles with a film thickness of commercially satisfactory uniformity.

Another object of this invention is to apply a a coating to surfaces ofopen-work articles electrostatically whose film thickness is ofcommercially acceptable uniformity.

A further object of this invention is to provide novel electrostaticapparatus for applying a coa ing of improved uniformity to round orwheelshaped articles.

Still another object of this invention is to provide novel electrostaticapparatus for applying a coating of improved uniformity to a surface ofa supported article adjacent its support.

A further object of this invention is to apply a coating of commerciallysatisfactory uniformity to a downwardly presented surface withelectrostatically atomized coating material.

In one embodiment of my invention for coating a three dimensionalarticle, such as an automobile steering wheel, one dimension of which ismaterially less than the other two, there is provided an apparatus whichcomprises a support for holding the article to maintain its larger planedefined by the two greatest dimensions in a predetermined position. Thisapparatus also includes an electrostatic atomizing head, means forsupplying liquid coating material to the atomizing head, means includinga high voltage source for establishing a high potential diiferencebetween the liquid coating material on the atomizing head and thearticle for electrostatically atomizing the coating material andelectrostatically depositing the atomized coating material on thearticle, and means for supporting the head in spaced relation from thearticle. This head support is constructed to permit arranging the headso that there is an angle of approximately 30 degrees between the axisof the head and a perpendicular to the larger plane of the article whichintersects the head axis at the larger plane. This angle may be a fewdegrees above or below thirty degrees, but I have found that if theangle is less than twenty degrees or more than forty degrees the desiredresults are not obtained. Also the head is so supported that its axis,when projected, passes through the article as it is moved past the head.

The invention will now be described with reference to the drawing ofwhich:

Figure 1 is a top plan view of apparatus for coating automobile steeringwheels and Figure 2 is an end elevation view taken on line 2--2 ofFigure 1.

Referring more specifically to the drawing, there is shown a pluralityof articles 10, illustrated as automobile steering wheels, supported onspaced spindles l2 rotatably connected to conveyor l4. Each spindle I2is provided with a pulley I6 which is adapted to be brought intoengagement with movable belt it to rotate the supported articles I0while they are moved by the conveyor.

The conveyor Ill is arranged to move the articles In over apredetermined path in the direction of the arrow 2%? past and in spacedrelation to an electrostatic atomizing device generally indicated by thenumeral 22.

The atomizing device comprises base 24, a standard 26, arm 28 andatomezing head lit. The standard 26 is mounted on the base 24 to movevertically and may be fixed in any desired position by knob 32. The arm28 is pivotally connected to the standard 26 at 3% and may be fixed inany desired position. The arm is constructed of electrically insulatingmaterial to isolate the head 3%! from ground. The head 3!) is adapted tobe rotated by being geared to a rotatable shaft (not shown) in thehollow arm 28, which may be driven by any suitable means such as themotor at 34. The head 30 is arranged so that its axis is at right anglesto the extent of the arm 28. The head 30 may be of any suitableconstruction. One such head is described in French Patent No. 982,327,published June 8, 1951. The head 30 shown comprises a shaft 3! and aflaring, recessed, conical bell 33 afiilxed to one end of the shaft. Theshaft 3i is provided with an axial passage (not shown) which at one endcommunicates with the pipe 36 and at the other end communicates with theapex at the interior of the conical bell 33. Liquid coating materialsuch as paint, lacquer or varnish is supplied to the conical bell 33from a source (not shown) through pipe 36 and the passage in the shaft3i. Rotation of the head 30 distributes the liquid fed to the bell 33 inthe form of a free-surfaced film over its inner surface and flows to itsouter peripheral edge 35. A high potential difference for example 90kilovolts D. C. is maintained between the liquid coating materialsupplied to the atomizing bell 33 and the articles I by connecting thehead to one terminal of a high voltage source 38 by means of conductor40. The other terminal of the high voltage source is grounded as is theconveyor Id.

In operation the articles ID are supported on the spindles l2 of theconveyor 14 so that they are maintained in position so that their largerplanes are in horizontal positions. These articles are moved by theconveyor I4 over a predetermined path past the atomizing device 22 forbeing coated thereby. In order to obtain the desired distribution ofcoating material on portions of the articles I B, the head 33 isarranged so that it is below and to one side of the articles H] as theymove past the head, and the head is sufficiently spaced from theconveyor [4 and articles ID to avoid sparking. Also the head 30 is soarranged that the axis of the head or spray is at an angle ofapproximately 30 degrees to the vertical and, when projected, this axispasses within the bounds of the articles as they move past the head.While I have obtained excellent results with the axis of the headarranged at 30 degrees to the vertical, satisfactory results are alsoobtainable if this angle is not less than degrees or more than 40degrees.

While I have shown and described one particular embodiment of myinvention, it is to be understood that it is capable of manymodifications. Changes, therefore, in the construction and arrangementmay be made without departing from the spirit and scope of the inventionas disclosed in the appended claims.

I claim:

1. In apparatus for electrostatically coating a series of similarthree-dimensional articles in each of which one of the three mutuallyperpendicular over-all dimensions is materially less than either of theother two, means for moving the articles translationally over apredetermined path in a coating zone, said article moving meansincluding supports for holding the articles with the sides defined bythe two greatest dimensions in generally horizontal positions, anelectrostatic atomizing head, means for supplying liquid coatingmaterial to said head, means including a high voltage source forestablishing an electrostatic field of sufificient strength between theliquid coating material on said head and the articles forelectrostatically atomizing the coating material from said head andelectrostatically depositing the coating material on the articles in thecoating zone, means for supporting said head spaced from the path ofarticle movement with the axis of said head lying in a plane normal tothe article path and with the axis of said head being at an angle ofapproximately 20 to 40 degrees to the vertical and passing within thebounds of the articles as they move past said head, and means forrotating the articles during at least aportion of the translationalmovement in the coating zone.

2. In apparatus for electrostatically coating a series of similarthree-dimensional open-work articles in each of which one of the threemutually perpendicular over-all dimensions is materially less thaneither of the other two, means for moving the articles over apredetermined path, said means including supports for holding thearticles with the sides defined by the two greatest dimensions ingenerally horizontal positions, an electrostatic atomizing head, meansfor supplying liquid coating material to said head, means including ahigh voltage source for es tablishing an electrostatic field ofsufficient strength between the liquid coating material on said head andthe articles for electrostatically atomizing the coating material fromsaid head and electrostatically depositing the coating material on thearticles, and means for supporting said head spaced from the path ofarticle movement below and to one side thereof and with the axis of saidhead being at an angle of approximately 30 degrees to the vertical andpassing within the bounds of the articles as they move past said head.

3. In apparatus for electrostatically coating a three-dimensionalarticle in which one of the three mutually perpendicular over-alldimensions is materially less than either of the other two, means forsupporting the article to maintain the larger sides defined by the twogreatest dimensions in predetermined positions, means for rotating thesupported article, an electrostatic atomizing head, means for supplyingliquid coating material to said head, means including a high voltagesource for establishing an electrostatic field of suflicient strengthbetween the liquid coating material on said head and the article forelectrostatically atomizing the coating material from said head andelectrostatically depositing the coating material on the article, andmeans for supporting said head spaced from the article and to one sideof one or said larger sides, said head being so arranged that there isan angle of approximately 20 to 40 degrees between the axis of said headand a line generally perpendicular to one of said larger sides.

4. In apparatus for electrostatically coating a three-dimensionalarticle in which one of the three mutually perpendicular over-alldimensions is materially less than either of the other two, a supportfor the article to maintain the sides of the article defined by its twogreatest dimensions generally perpendicular to the longitudinal axis ofsaid article support, an electrostatic atomizing head, means forsupplying liquid coating material to said head, means including a highvoltage source for establishing an electrostatic field of sufficientstrength between the liquid coating material on said head and thearticle for electrostatically atomizing the coating material from saidhead and electrostatically depositing the atomized coating material onthe article, and means for supporting said head spaced from the articleand its support and on the same side of said article as is said articlesupport, said head being so arranged that there is an angle ofapproximately 20 to 40 degrees between the axis of said head and thelongitudinal axis of said article support.

5. Apparatus for electrostatically coating a plurality of similarthree-dimensional articles in each of which one of the three mutuallyperpendicular overall dimensions is materially less than either of theother two, comprising a conveyor for moving the articles over apredetermined path, said articles being oriented on said conveyor sothat a side of each article defined by its two greatest dimensions movesgenerally in the same predetermined plane, means for creating a spray ofcharged coating material particles at a point spaced from said conveyor,said spray creating means being spaced close enough to the article pathto envelop the articles with the spray as they move past said spraycreating means and being arranged so that its axis lies in a planegenerally transverse to the article path and is at an angle ofapproximately 20 to 40 degrees to a perpendicular to said predeterminedplane, and means for establishing an electrostatic field between saidspray creating means and the articles, said field being substantiallythe sole medium for depositing the spray onto the articles.

6. Apparatus for coating a plurality of automobile steering wheels orlike articles, comprising a conveyor including suitable workholders formoving said wheels along a predetermined path with their faces arrangedhorizontally, an atomizing head spaced from said wheels for creating aspray of coating material particles, said head being arranged with itsaxis lying in a plane generally transverse to the conveyor path and atan angle of 20 to degrees to the vertical, a projection of said axispassing through the bounds of the wheels moving past said head, andmeans including a source of high electrical potential for establishingan electrostatic field between said head and the wheels of suflicientstrength to charge the coating material particles, move them from saidhead and deposit them onto the wheels as a coating.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,239,695 Bennett Apr. 29, 1941 2,555,519 Tolle et al June 5,1951 2,567,781 Ransburg Sept. 11, 1951 FOREIGN PATENTS Number CountryDate 982,327 France Jan. 24, 1951

